Known in-wheel motor drive devices are often used to individually driven right and left wheels of an electric vehicle by mounting their electric motors in the wheel bodies of the right and left wheels, respectively. Since use of such in-wheel motor drive devices eliminates the necessity of a differential gear mechanism and a driven shaft, it minimizes energy loss during transmission of power. Since the driving forces of the right and left wheels are individually controlled by the electric motors mounted in the respective wheels, it is possible to improve travel stability of the vehicle.
Such an in-wheel motor drive device is known from the below-identified Patent document 1. The in-wheel motor drive device disclosed in Patent document 1 includes a hub to which is mounted the wheel body of a wheel; an electric motor arranged inside of the hub in the width direction of the vehicle; a speed reducer for reducing and transmitting the rotation of the electric motor to the hub; and a motor housing in which are received the electric motor and the speed reducer. A hub bearing is mounted on the motor housing at its outer end in the width direction of the vehicle to rotatably support the hub.
In a vehicle including an in-wheel motor drive device of this type, it is difficult to mount and dismount a brake caliper of a disk brake, for the following reasons.
The disk brake includes a brake disk mounted to the hub so as to rotate together with the hub, and a brake caliper configured to clamp the brake disk through a pair of brake pads. In a vehicle including no in-wheel motor, the brake caliper is fixed in position by driving bolts in the direction parallel to the axis of the brake disk, from inside in the width direction of the vehicle (see, for example, the below-identified Patent document 2).
The reason why the bolts are driven in from inside, and not from outside, in the width direction of the vehicle is because the brake disk is in the way if an attempt is made to drive the bolts from outside in the width direction of the vehicle. The brake caliper is therefore typically designed such that it can be fixed in position by driving bolts from inside in the width direction of the vehicle.
However, in a vehicle including an in-wheel motor drive device, since its electric motor and speed reducer are arranged inside the brake disk in the width direction of the vehicle, the electric motor and the speed reducer will be in the way when the bolts are driven in from inside in the width direction of the vehicle, thereby making it difficult to mount and dismount the brake caliper.
In the in-wheel motor drive device disclosed in Patent document 1, in order to more easily mount and dismount the brake caliper, the brake disk is formed with through holes through which bolts can be inserted so that by inserting the bolts and a tool through the through holes, the bolts can be driven in, in the direction parallel to the axis of the brake disk from outside in the width direction of the vehicle, whereby the brake caliper is fixed to the motor housing at its axial end surface by driving the bolts.